This invention relates to decorative mouldings and more particularly to a method and apparatus for coating preformed workpieces having decorative surfaces.
Preformed workpieces such as decorative mouldings are widely used in the construction industry. Such mouldings are designed to be mounted against exterior or interior walls for providing architectural features on building structures in sectors such as residential, industrial, commercial and institutional buildings. The exposed surface of the moulding is usually decorative and as such, has an irregular surface in cross-section and continuous in the longitudinal direction. Mouldings can be fabricated from several materials including wood, plaster and expanded polystyrene (EPS). EPS mouldings are particularly attractive to use because of their relatively light weight and ease of fabrication. In order that the moulding be both attractive and durable, moulding substrates or workpieces are typically coated with various coating materials to provide an attractive finish to the product. Traditionally, mouldings have been coated by hand after the EPS moulding is secured to the exterior of the structure. This involved applying with hand tools, a layer of base coat to the moulding and then embedding a fiberglass mesh onto the moulding and allowing it to dry. A layer of stucco or special paint as a finish coat is usually subsequently applied to the base coated moulding after the moulding is installed. This method is very labor intensive and consequently, very slow and expensive. Often times, the quality of the applied base coating is not consistent due to poor workmanship. This results in a coating of uneven thickness which eventually cracks and does not look very attractive.
More recently, various types of automated equipment have been designed to apply coatings to different types of workpieces. For example, U.S. Pat. No. 5,514,417 discloses a method and apparatus for coating a molded fibrous workpiece with a foam material. In this method and apparatus, the workpiece is passed through a foam bath within a coating chamber. To ensure a good coating of the workpiece, the foam material is spread over the entire exterior surface of the workpiece using wipers within the coating bath.
Canadian patent 2,184,205 discloses a method and apparatus for applying a coating material onto the surface of a decorative workpiece. In this method, the workpiece is slid through a bath of coating material contained within a coating chamber where the coating material is applied simply under the weight of the material. The workpiece is slidingly advanced on a continuous flat platform by a set of guide rollers abutting both sides of the workpiece both before and after passing through the coating bath while simultaneously shielding the bottom surface of the workpiece. This method and apparatus does provide a coating on the decorative surface of the workpiece, however, the resultant coating may be inconsistent with respect to its thickness. This is partly due to the fact that the workpiece moves and slides about on the platform as it is being guided into the coating chamber. This is also true when the workpiece exits the coating bath, as lateral, horizontal and vertical movement will result in varying thicknesses of coating material being applied to the surface of the workpiece as it exits the coating bath. Furthermore, once in the coating chamber, the coating material may not be evenly distributed onto the intricate curves present on the exterior design of the workpiece. The coating material can bubble on the surface of the workpiece due to having the workpiece pass through a bath of thick, viscous coating material at varying speeds which results in different rates of shear of the material at the bath exit. Consequently, parts of the workpiece will not be coated adequately or not at all. Once the workpiece exits the bath, it may not be allowed to dry sufficiently before the guide rollers, continue to advance it forward and thus contact the wet coated workpiece and possibly damage its coating. Also, it is required that the coated mouldings air dry for at least 24 hours.
There is therefore a need to develop a novel method and apparatus for coating decorative workpieces used widely in various construction sectors, in a consistent, simple, efficient manner such to provide a smooth durable coating distributed in a controlled manner to desired exposed decorative surfaces of a workpiece. There is also a need to provide a finished coated workpiece which has a smooth, exterior coating finish which is aesthetically pleasing as well as very durable and thus resistant to damage.
In accordance with the present invention there is provided a method and apparatus for applying a coating material to the decorative exposed surface of a preform workpiece. Both the method and apparatus provide on a consistent basis, a smooth durable coating with a controlled desired thickness to the entire exposed decorative surface of a workpiece. The coating as applied to the surface of the workpiece is tightly bonded thereto such that it cannot be removed therefrom without causing damage to the workpiece itself. The coating material is a plaster-like coating material and can be selected from cement based and polymeric based materials as is known to those skilled in the art.
The method and apparatus avoid the problems of having air bubbles in the finished coating, delamination of the coating from the workpiece, the appearance of cracks in the coating or an uneven thickness of coating material left on the coated workpiece. The method and apparatus are relatively simple, efficient and cost effective and reliably on a consistent basis provide a means for applying a plaster-like coating to the exposed decorative surface of a workpiece on a commercial scale for use in the construction industry.
According to an aspect of the present invention there is provided an apparatus for applying a coating material to exposed surfaces of a preform workpiece having a decorative exposed surface and a bottom portion, said apparatus comprising:
means for mechanically advancing a workpiece along said apparatus along a straight horizontal axis over a non-continuous surface;
means for engaging the bottom portion of a workpiece to constrain lateral and vertical movement as the workpiece passes along said apparatus; and
means for applying a desired thickness of coating material to a decorative surface of an advancing workpiece.
Preferably, the decorative preform workpiece has a mesh laminated to its decorative surface prior to being advanced through a coating chamber.
In one embodiment of the invention, the coating means is also adapted to apply a coating to the bottom outside edges of the bottom portion of the workpiece.
According to a further aspect of the invention is a method for applying a coating material to exposed surfaces of a preform workpiece having a decorative exposed surface and a bottom portion, said method comprising the steps of:
continuously advancing said workpiece in a straight horizontal axis via engagement of said workpiece by its bottom portion to prevent lateral and vertical movement of said workpiece as it is being advanced;
applying a plaster-like coating material to the exposed irregular decorative surface of the advanced workpiece; and
advancing the coated workpiece through a die opening closely conforming to the cross-sectional profile of the workpiece, wherein the cross sectional size of the die opening relative to the cross sectional size of the workpiece determines the thickness of the plaster-like coating material left remaining on the decorative surface of the coated workpiece.
According to yet a further aspect of the invention is a method for applying a coating material to exposed surfaces of a preform workpiece having a decorative exposed surface and a bottom portion, said method comprising the steps of:
providing a workpiece having a thin mesh laminated to its entire decorative surface and to the outer bottom edges of the bottom portion of the workpiece;
continuously advancing said workpiece in a straight horizontal axis wherein said workpiece is engaged via its bottom portion to prevent lateral and vertical movement of said advancing workpiece;
applying a coating material to the exposed irregular decorative surface of the workpiece; and
advancing the coated workpiece through a die opening closely conforming to the cross-sectional profile of the workpiece, wherein the cross sectional size of the die opening relative to the cross sectional size of the workpiece determines and controls the thickness of the plaster-like coating material left remaining on the decorative surface of the coated workpiece.
According to still a further aspect of the invention is a method for bonding a coating material to desired exposed surfaces of a preform workpiece having a decorative exposed surface and a bottom portion, said method comprising;
anchoring a thin mesh to the entire decorative surface of the workpiece and to the outer bottom edges of the bottom portion of the workpiece; and
applying a coating material under pressure to said anchored mesh to bond said mesh to said decorative exposed surface and to the outer bottom edges of the bottom portion of the workpiece, wherein said bonding creates a finished smooth protective coating on said workpiece.
Preferably, the bonding method is a two step process wherein the first step applies a coat of coating material which completely submerges the mesh and anchors it into the surface of the workpiece. The second step of the process provides a top coat of coating material which provides a smooth attractive durable finish. Typically, the first step provides a thicker coating of coating material and the second step provides a thinner coating material compared to the first step. If desired, additional thin layers of coating material can be applied to a coated workpiece.
According to yet another aspect of the invention is a preform workpiece comprising;
an elongate body having an exposed decorative surface and a substantially flat bottom portion; and
means for facilitating the adherence of a coating material to the exposed decorative surface of said workpiece.
According to yet a further aspect of the present invention is a coated workpiece comprising;
a preformed workpiece having a decorative exposed surface with a plurality of spaced apart surface grooves orientated longitudinally along the length of said workpiece and a substantially flat bottom portion;
a mesh laminated to the exposed surface and partially about bottom outside edges of bottom portion of said workpiece; and
at least one layer of a coating material bonding said mesh to the exposed decorative surface and to bottom outside edges of the bottom portion of said workpiece, wherein the coating material impregnates the mesh and anchors said mesh within said surface grooves within said decorative exposed surface such that the mesh and coating material are firmly bonded to the decorative surface of the workpiece. In one embodiment a thin layer of coating material may also impregnate and anchor the mesh located about the bottom outside edges of the bottom portion of said workpiece.
Both the preform workpiece and the coated workpiece may additionally have a means for mounting such workpieces to a desired surface located in the flat bottom portion.
Both the preform workpiece and the coated workpiece may additionally have a means for mounting such workpieces to a desired surface located in the flat bottom portion.